This document discusses the ongoing drought conditions in California and compares them to previous drought periods. It finds that 21st century droughts have been warmer and more severe than those in the 20th century, with lower snowpack levels and runoff amounts. California's precipitation is also highly variable from year to year and from decade to decade. The current drought is comparable to some of the most severe droughts on record dating back to the 16th century. Atmospheric river events are important for precipitation but have been less common during drought years. Going forward, more extreme variability in the climate is expected and planning will need to account for the possibility of even worse drought conditions than what the historical record shows.

1. CA Drought Update 2015
US Drought Monitor Forum
April 16, 2015
Oroville Reservoir January 2009

2. Presentation Overview
• Current Drought Conditions
• Variability
Folsom Reservoir January 2014

3. California’s topography
affects our weather and climate

4. 0
10
20
30
40
50
60
70
80
50 51 52 53 54 55 56 57 58
AnnualPrecipitation(inches)
Annual Average Temperature (deg F)
1895-2000 21st Century POR Average
2
Source: NOAA Climate Division 2 Calendar Year Data
2014
It’s Getting Warmer
2013
2012

5. April –July Runoff (million acre-feet)
WaterYearRunoff(millionacre-feet)
21st Century Droughts on the Sacramento River
1976
2
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16
20th Century 21st Century POR Average
5 of 20 lowest April-July flows since 2001

6. 0
5
10
15
20
25
30
35
40
45
52 53 54 55 56 57 58 59 60 61
AnnualPrecipitation(inches)
Annual Average Temperature (deg F)
1895-2000 21st Century POR Average
2
Source: NOAA Climate Division 5 Calendar Year Data
2014
2013
5
It’s Getting Warmer
2012

7. April –July Runoff (million acre-feet)
WaterYearRunoff(millionacre-feet)
21st Century Droughts on the San Joaquin River
1976
2
5 of 20 lowest April-July flows since 2001
0
2
4
6
8
10
12
14
16
0 2 4 6 8 10
1901-2000 2001-2014 POR Average

14. Worst April 1 Snowpacks
2015 5 percent
2014 25
1977 25
1988 29
1976 37
2007 39
2013 42
1963 45
1990 45
1994 52
2012 52

15. Year to Year Precipitation Variability
Dettinger et al, 2011
Std Dev of Annual Precipitation
Mean Annual Precipitation
California precipitation
is uniquely variable
Higher values are higher variability

16. 0
10
20
30
40
50
60
70
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Los Angeles County Sonoma Mendocino 8 Station Index 5 Station Index
Decadal Scale Variability

17. Comparison of WSI - Sacramento
Water Year
Type 1924-1938 21st Century
W 2 2
AN 1 2
BN 3 3
D 4 5
C 5 3
Includes forecast of critical for 2015

18. Comparison of Runoff – Sacramento
21st Century Oct-Mar Apr-Jul WY
Max 18.06 13.09 32.09
Average 8.66 6.08 15.48
Min 4.29 2.6 7.47
1923-1940 Oct-Mar Apr-Jul WY
Max 17.96 12.93 31.83
Average 7.63 5.87 14.13
Min 3.27 1.94 5.74
Units are Million Acre-Feet

19. * From tree rings
18.6
8.7*
12.0
11.2
9.8
13.1
12.4
6.7
10.0
11.2
10.4
0
5
10
15
20
WY
Average
1578-1580 1918-1920 1924-1926 1929-1934 1947-1950 1959-1961 1976-1977 1987-1992 2007-2009 2012-2014
SACRAMENTO FOUR RIVER RUNOFF
COMPARISON WITH PREVIOUS DROUGHTS
Average Annual Drought Period Runoff in Million Acre-Feet

20. Comparison of WSI - San Joaquin
Water Year
Type 1924-1938 21st Century
W 2 3
AN 4 1
BN 2 2
D 2 4
C 5 5
Includes forecast of critical for 2015

21. Comparison of Runoff – San Joaquin
21st Century Oct-Mar Apr-Jul WY
Max 3.68 7.37 10.99
Average 1.55 3.41 5.08
Min 0.46 1.21 1.72
1924-1938 Oct-Mar Apr-Jul WY
Max 3.58 7.33 11.24
Average 1.33 3.38 4.80
Min 0.45 1.03 1.5
Units are Million Acre-Feet

22. * From tree rings
6.0
2.3*
4.3
3.5 3.3
4.0
2.7
1.5
2.7
3.7
2.5
0
2
4
6
WY
Average
1653-1655 1918-1920 1924-1926 1929-1934 1947-1950 1959-1961 1976-1977 1987-1992 2007-2009 2012-2014
SAN JOAQUIN FOUR RIVER RUNOFF
COMPARISON WITH PREVIOUS DROUGHTS
Average Annual Drought Period Runoff in Million Acre-Feet

23. Storm Track changes
Flooding &
water supply
MJO/Tropical
Convection ENSO
Polar Processes
Key Phenomena Affecting California
Water Supply/Flooding:
Easterly Wave
Cyclogensis
L
The size of the AR results from the
alignment of key processes
The absence of AR activity important to drought

24. Summarizing Thoughts
• 21st century droughts have shown record
setting characteristics and are warmer than
20th century counterparts
• Atmospheric river events provide significant
inputs into annual precipitation totals – fewer
such events in drought years

25. Conclusions
• The expectation of increased variability means
new extremes and extreme transitions with past
few years serving as an example.
• Planning for future droughts can take advantage
of information in the historical record including
paleo reconstructions. The trick will be to
increase our understanding of causal
mechanisms and watershed condition/response.

26. Questions?
Email: Michael.L.Anderson@water.ca.gov